Speedo Off w/ SCT Tune - Mustang Evolution

Go Back   Mustang Evolution > 1979-2015 Mustang GT || Tech and Talk > 2005-2010 Mustang GT



Reply
 
Thread Tools Search this Thread
Please support our sponsors and let them know you heard about them here!
Old 02-27-2012, 11:42 AM   #1
Registered Member
Regular
 
Aggiesrok's Avatar
 
Join Date: Jul 2011
Location: Bryan
Region: Texas
Posts: 1,883
Speedo Off w/ SCT Tune

I've updated the tuner with the latest firmware and tuner version. I entered my rearend 3.55 and my revs/mile 740 and my speedo is off about 10%. I checked it with a GPS app. The app is dead on in my wife's Explorer but off 10% in my 07 mustang GT. Any ideas?
Aggiesrok is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 02-27-2012, 08:29 PM   #2
Registered Member
Regular
 
Aggiesrok's Avatar
 
Join Date: Jul 2011
Location: Bryan
Region: Texas
Posts: 1,883
Nobody got nothing?
__________________
chevy runs deep, Don't step in chevy!

289 - Holley 4150 570cfm; Performer intake; mild cam; MSD HEI; 302 heads; Roller Tips; Hedman Tri-Y headers; H-pipe w/Flowmaster 40's; 9 in posi 3.50; 205/50-17F; 225/50-17R.
Aggiesrok is offline   Reply With Quote
Old 02-27-2012, 09:06 PM   #3
Registered Member
Regular
 
irishn8's Avatar
 
Join Date: Jan 2012
Region: Washington
Posts: 721
I got the same problem bro... idk wtf
irishn8 is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 02-27-2012, 09:21 PM   #4
Registered Member
Regular
 
Charles.young10's Avatar
 
Join Date: Jan 2012
Region: Oklahoma
Posts: 299
The only thing I can think of...

What tire size? That can mess things up.. I'm sure you know
Charles.young10 is offline   Reply With Quote
Old 02-27-2012, 09:23 PM   #5
Registered Member
Regular
 
irishn8's Avatar
 
Join Date: Jan 2012
Region: Washington
Posts: 721
Ya that's why we set the Revs-per-mile.
irishn8 is offline   Reply With Quote
Old 02-27-2012, 09:27 PM   #6
Registered Member
Regular
 
Charles.young10's Avatar
 
Join Date: Jan 2012
Region: Oklahoma
Posts: 299
Quote:
Originally Posted by irishn8
Ya that's why we set the Revs-per-mile.
Custom rims? You may have to calculate it yourself if it changed the standard diameter
Charles.young10 is offline   Reply With Quote
Old 02-27-2012, 09:29 PM   #7
Registered Member
Regular
 
Aggiesrok's Avatar
 
Join Date: Jul 2011
Location: Bryan
Region: Texas
Posts: 1,883
Yeah I've stock rims for CS. 235/50/18 which calculates to 740 revs per mile.
__________________
chevy runs deep, Don't step in chevy!

289 - Holley 4150 570cfm; Performer intake; mild cam; MSD HEI; 302 heads; Roller Tips; Hedman Tri-Y headers; H-pipe w/Flowmaster 40's; 9 in posi 3.50; 205/50-17F; 225/50-17R.
Aggiesrok is offline   Reply With Quote
Old 02-27-2012, 09:32 PM   #8
Registered Member
Regular
 
Charles.young10's Avatar
 
Join Date: Jan 2012
Region: Oklahoma
Posts: 299
Quote:
Originally Posted by Aggiesrok
Yeah I've stock rims for CS. 235/50/18 which calculates to 740 revs per mile.
Ah! Yeah stock rims shouldn't be a problem.. Dont know then.. Sorry.. That was the only thing I could think of
Charles.young10 is offline   Reply With Quote
Old 02-27-2012, 09:38 PM   #9
Registered Member
Regular
 
irishn8's Avatar
 
Join Date: Jan 2012
Region: Washington
Posts: 721
Quote:
Originally Posted by Charles.young10

Custom rims? You may have to calculate it yourself if it changed the standard diameter
Nah doesn't matter, revs per mile is just how many times a given point on the outermost part of the tire makes one complete revolution in a mile.

However, now that I think about it, a tire doesn't maintain its shape completely, it always has that flat part on the ground. So its like having a slightly smaller tire...dude that's gotta be it! Right?
irishn8 is offline   Reply With Quote
Old 02-27-2012, 09:51 PM   #10
Registered Member
Regular
 
Charles.young10's Avatar
 
Join Date: Jan 2012
Region: Oklahoma
Posts: 299
Quote:
Originally Posted by irishn8
Nah doesn't matter, revs per mile is just how many times a given point on the outermost part of the tire makes one complete revolution in a mile
So your trying to tell me a bigger diameter tire wont change that?

Here maybe this will help..

http://wiki.answers.com/Q/Will_the_s...on_larger_rims
Charles.young10 is offline   Reply With Quote
Old 02-27-2012, 10:00 PM   #11
Registered Member
Regular
 
irishn8's Avatar
 
Join Date: Jan 2012
Region: Washington
Posts: 721
If u got a bigger diameter tire and DIDN'T set the revs per mile then ya it would effect that.
irishn8 is offline   Reply With Quote
Old 02-27-2012, 10:00 PM   #12
Registered Member
Regular
 
Aggiesrok's Avatar
 
Join Date: Jul 2011
Location: Bryan
Region: Texas
Posts: 1,883
Even a full inch change in diameter only yields a 2 mph error.

I'm getting new tires this week, so we'll see if that has an effect.
__________________
chevy runs deep, Don't step in chevy!

289 - Holley 4150 570cfm; Performer intake; mild cam; MSD HEI; 302 heads; Roller Tips; Hedman Tri-Y headers; H-pipe w/Flowmaster 40's; 9 in posi 3.50; 205/50-17F; 225/50-17R.
Aggiesrok is offline   Reply With Quote
Old 02-27-2012, 10:06 PM   #13
Registered Member
Regular
 
irishn8's Avatar
 
Join Date: Jan 2012
Region: Washington
Posts: 721
Quote:
Originally Posted by Aggiesrok
Even a full inch change in diameter only yields a 2 mph error.

I'm getting new tires this week, so we'll see if that has an effect.
Sounds right to me, my speedo is off by about 2mph I have 275/40 17s equates to 786 rpMi
irishn8 is offline   Reply With Quote
Old 02-28-2012, 09:30 AM   #14
Registered Member
Regular
 
Aggiesrok's Avatar
 
Join Date: Jul 2011
Location: Bryan
Region: Texas
Posts: 1,883
Re: Speedo Off w/ SCT Tune

Quote:
Originally Posted by irishn8 View Post
Sounds right to me, my speedo is off by about 2mph I have 275/40 17s equates to 786 rpMi
But that doesn't solve the problem. It means that our tires would have to be over 4 inches smaller than stated in order to be off by over 5 mph at 60.

Does anyone with a Bama tune have this problem? Mine is a SCT tune.
Aggiesrok is offline   Reply With Quote
Old 02-28-2012, 09:41 AM   #15
Registered Member
Regular
 
Charles.young10's Avatar
 
Join Date: Jan 2012
Region: Oklahoma
Posts: 299
Quote:
Originally Posted by Aggiesrok

But that doesn't solve the problem. It means that our tires would have to be over 4 inches smaller than stated in order to be off by over 5 mph at 60.

Does anyone with a Bama tune have this problem? Mine is a SCT tune.
I know the 410 guys have problems, but 355 are/can be stock gears.. You really shouldn't have any problems
Charles.young10 is offline   Reply With Quote
Old 02-28-2012, 10:52 AM   #16
Moderator Emeritus
Legacy
Regular
 
SpectorV's Avatar
 
Join Date: May 2003
Region: Alabama
Posts: 26,049
Send a message via AIM to SpectorV
Re: Speedo Off w/ SCT Tune

generally sct lets you enter rotations per mile not just XX gearing right?
__________________
2003 Cobra Vert (Redfire) #3938 of 5082 @ 05/27/2003
472rwhp/493rwtq -Modification List - Dyno Sheet
2012 Mustang 3.7L M6 (Kona Blue)
2011 Ford Edge Sport (Red Metallic)
SpectorV is offline   Reply With Quote
Old 02-28-2012, 11:26 AM   #17
Registered Member
Regular
 
Aggiesrok's Avatar
 
Join Date: Jul 2011
Location: Bryan
Region: Texas
Posts: 1,883
Re: Speedo Off w/ SCT Tune

Quote:
Originally Posted by SpectorV View Post
generally sct lets you enter rotations per mile not just XX gearing right?
Yeah I can enter axle ratio and revs per mile. But it doesnt seem to be factored in.
Aggiesrok is offline   Reply With Quote
Old 02-28-2012, 11:39 AM   #18
Registered Member
Regular
 
RedGT's Avatar
 
Join Date: Jan 2012
Region: Canada
Posts: 102
Try to get the builder to program the different gear ratio and tire size into the tune. They should be able to do that. Or try to change the settings again. Maybe it didn't save. Not overly helpful I know but it's better than nothing.
RedGT is offline   Reply With Quote
Old 02-28-2012, 02:59 PM   #19
Registered Member
Regular
 
Aggiesrok's Avatar
 
Join Date: Jul 2011
Location: Bryan
Region: Texas
Posts: 1,883
Re: Speedo Off w/ SCT Tune

So if I fake out the speedo by putting the wrong revs/mile number for the tire size, in order to get the correct speedo reading, will this have any affect on the tune?

i.e. does the tire size factor into anything besides the speedo calc?
Aggiesrok is offline   Reply With Quote
Old 02-29-2012, 08:54 AM   #20
Registered Member
Regular
 
RedGT's Avatar
 
Join Date: Jan 2012
Region: Canada
Posts: 102
Quote:
Originally Posted by Aggiesrok
So if I fake out the speedo by putting the wrong revs/mile number for the tire size, in order to get the correct speedo reading, will this have any affect on the tune?

i.e. does the tire size factor into anything besides the speedo calc?
I highly doubt it. The tune isn't something you can change on the tuner. The tune has fuel and air ratio settings, throttle response, etc. The tire size doesn't change those factors. Another dumb question, you sure you got the right revs/mile?
RedGT is offline   Reply With Quote
Old 02-29-2012, 10:41 AM   #21
Registered Member
Regular
 
Aggiesrok's Avatar
 
Join Date: Jul 2011
Location: Bryan
Region: Texas
Posts: 1,883
Re: Speedo Off w/ SCT Tune

Quote:
Originally Posted by RedGT View Post
I highly doubt it. The tune isn't something you can change on the tuner. The tune has fuel and air ratio settings, throttle response, etc. The tire size doesn't change those factors. Another dumb question, you sure you got the right revs/mile?
Yeah I've checked that numerous times. 235/50/18 = 740 revs per mile.
Aggiesrok is offline   Reply With Quote
Old 02-29-2012, 11:44 AM   #22
Registered Member
Regular
 
RedGT's Avatar
 
Join Date: Jan 2012
Region: Canada
Posts: 102
Quote:
Originally Posted by Aggiesrok

Yeah I've checked that numerous times. 235/50/18 = 740 revs per mile.
News flash dude. I'm getting 763.3 revs/mile. Check out 1010tire.com and tirerack.com. I think your source of info might be the problem.
RedGT is offline   Reply With Quote
Old 02-29-2012, 12:10 PM   #23
Registered Member
Regular
 
Aggiesrok's Avatar
 
Join Date: Jul 2011
Location: Bryan
Region: Texas
Posts: 1,883
Re: Speedo Off w/ SCT Tune

Quote:
Originally Posted by RedGT View Post
News flash dude. I'm getting 763.3 revs/mile. Check out 1010tire.com and tirerack.com. I think your source of info might be the problem.
I get close to 740 when doing the math, but on tirerack they seem to calculate the revs while taking into consideration the flattening on the ground and not purely by math. Their calculation for my stock tire is 759 and with little tread left, it would be even higher. I'm getting 255/45/18's this Friday and I'll try the tirerack calc of 773 for those and see what happens. After all this, as tires lose inflation, your speedo would begin to give an increased reading.

Thanks for the effort, it seems to be the right answer.
Aggiesrok is offline   Reply With Quote
Old 02-29-2012, 12:14 PM   #24
Registered Member
Regular
 
Charles.young10's Avatar
 
Join Date: Jan 2012
Region: Oklahoma
Posts: 299
Quote:
Originally Posted by Aggiesrok
So if I fake out the speedo by putting the wrong revs/mile number for the tire size, in order to get the correct speedo reading, will this have any affect on the tune?

i.e. does the tire size factor into anything besides the speedo calc?
Yes it will affect your odometer as well....
Charles.young10 is offline   Reply With Quote
Old 02-29-2012, 02:02 PM   #25
Registered Member
Regular
 
RedGT's Avatar
 
Join Date: Jan 2012
Region: Canada
Posts: 102
Quote:
Originally Posted by Aggiesrok

I get close to 740 when doing the math, but on tirerack they seem to calculate the revs while taking into consideration the flattening on the ground and not purely by math. Their calculation for my stock tire is 759 and with little tread left, it would be even higher. I'm getting 255/45/18's this Friday and I'll try the tirerack calc of 773 for those and see what happens. After all this, as tires lose inflation, your speedo would begin to give an increased reading.

Thanks for the effort, it seems to be the right answer.
No problem. Glad to get you an answer.
RedGT is offline   Reply With Quote
Old 02-29-2012, 04:12 PM   #26
Registered Member
Regular
 
Aggiesrok's Avatar
 
Join Date: Jul 2011
Location: Bryan
Region: Texas
Posts: 1,883
Re: Speedo Off w/ SCT Tune

Quote:
Originally Posted by RedGT View Post
No problem. Glad to get you an answer.
More evidence that you were correct.

I went and measured my tire from the ground to the center of the rim and multiplied that by 2 to get the true rolling diameter. After using that number and calculating the revs per mile, I get 784 revs per mile instead of the 740 entered into the tuner. This computes to be almost a 5 mph higher reading on the speedometer vs. actual speed.

Therefore if you want to get the correct speed, the formula is as follows:

63,360 / (2 * ∏ * r)

(5280 * 12) inches in a mile divided by (2 * ground to center of rim * ∏) circumference of wheel = revs per mile.
Aggiesrok is offline   Reply With Quote
Old 02-29-2012, 04:59 PM   #27
Registered Member
Regular
 
Charles.young10's Avatar
 
Join Date: Jan 2012
Region: Oklahoma
Posts: 299
Quote:
Originally Posted by Aggiesrok

More evidence that you were correct.

I went and measured my tire from the ground to the center of the rim and multiplied that by 2 to get the true rolling diameter. After using that number and calculating the revs per mile, I get 784 revs per mile instead of the 740 entered into the tuner. This computes to be almost a 5 mph higher reading on the speedometer vs. actual speed.

Therefore if you want to get the correct speed, the formula is as follows:

63,360 / (2 * ∏ * r)

(5280 * 12) inches in a mile divided by (2 * ground to center of rim * ∏) circumference of wheel = revs per mile.
Sorry but have to point out, I told you that yesterday......
Charles.young10 is offline   Reply With Quote
Old 02-29-2012, 06:08 PM   #28
Registered Member
Regular
 
Aggiesrok's Avatar
 
Join Date: Jul 2011
Location: Bryan
Region: Texas
Posts: 1,883
Re: Speedo Off w/ SCT Tune

Quote:
Originally Posted by Charles.young10 View Post
Sorry but have to point out, I told you that yesterday......
Sorry it didn't sink in until I heard it again and in a different way. Thanks.
Aggiesrok is offline   Reply With Quote
Old 02-29-2012, 06:19 PM   #29
Registered Member
Regular
 
Charles.young10's Avatar
 
Join Date: Jan 2012
Region: Oklahoma
Posts: 299
Quote:
Originally Posted by Aggiesrok

Sorry it didn't sink in until I heard it again and in a different way. Thanks.
Lol, not a big deal... Doesn't help when someone post stuff, and they don't know what they are talking about..
Charles.young10 is offline   Reply With Quote
Old 02-29-2012, 08:39 PM   #30
Registered Member
Regular
 
irishn8's Avatar
 
Join Date: Jan 2012
Region: Washington
Posts: 721
Quote:
Originally Posted by Aggiesrok

More evidence that you were correct.

I went and measured my tire from the ground to the center of the rim and multiplied that by 2 to get the true rolling diameter. After using that number and calculating the revs per mile, I get 784 revs per mile instead of the 740 entered into the tuner. This computes to be almost a 5 mph higher reading on the speedometer vs. actual speed.

Therefore if you want to get the correct speed, the formula is as follows:

63,360 / (2 * ∏ * r)

(5280 * 12) inches in a mile divided by (2 * ground to center of rim * ∏) circumference of wheel = revs per mile.
Cool so I had the right idea. Thanx for the formula, ill adjust my tuner and see what happens. Did it work for u?
irishn8 is offline   Reply With Quote
Old 02-29-2012, 09:16 PM   #31
Registered Member
Regular
 
Aggiesrok's Avatar
 
Join Date: Jul 2011
Location: Bryan
Region: Texas
Posts: 1,883
New tires Friday, so I'm going to wait. Unless I do it tomorrow just to test.
__________________
chevy runs deep, Don't step in chevy!

289 - Holley 4150 570cfm; Performer intake; mild cam; MSD HEI; 302 heads; Roller Tips; Hedman Tri-Y headers; H-pipe w/Flowmaster 40's; 9 in posi 3.50; 205/50-17F; 225/50-17R.
Aggiesrok is offline   Reply With Quote
Old 03-01-2012, 03:40 AM   #32
Registered Member
Regular
 
RVAStang05's Avatar
 
Join Date: Aug 2011
Region: Virginia
Posts: 323
I'm horrible at math, but thought I'd mention.. I went from the stock wheels 17" to 18" rims to 18" rims with 245/45-18 in front ( 275 in back). I had the SCT/bama tune already on when I switched wheels.

I've used 3 different gps/speedo apps on my phone to check accuracy and my spreedo is right on.
__________________
Pype Bomb Axle-Backs, JLT CAI, SCT Tuner w/Bama tuning, BMR Strut Tower Brace, CDC Classic Chin Spoiler, Black Hood Pins, Black Shorty antenna, Tru-Billet Black Anodized GT engraved Fuel Door, Black Lemans Stripes, Black Rocker Stripes, Brushed Aluminum finish dash and vents, Stack Racing pedals, Charcoal Black Leather Interior, Gloss Black Bullitt Motorsport Wheels, Nitto 555 tires, staggered set up (9/10), 35% tint, Shaker 1000 Stereo with Kicker Upgrades, Ultra Violet footwell, license plate and dome lighting
RVAStang05 is offline   Reply With Quote
Old 03-01-2012, 01:38 PM   #33
Registered Member
Regular
 
Aggiesrok's Avatar
 
Join Date: Jul 2011
Location: Bryan
Region: Texas
Posts: 1,883
Re: Speedo Off w/ SCT Tune

Quote:
Originally Posted by irishn8 View Post
Cool so I had the right idea. Thanx for the formula, ill adjust my tuner and see what happens. Did it work for u?
It worked! I had to try it before the new tires. I used the revs I calculated from measuring and it's dead on.
Aggiesrok is offline   Reply With Quote
Old 03-01-2012, 01:52 PM   #34
Registered Member
Regular
 
irishn8's Avatar
 
Join Date: Jan 2012
Region: Washington
Posts: 721
Awesome!
irishn8 is offline   Reply With Quote
Reply

Lower Navigation
Go Back   Mustang Evolution > 1979-2015 Mustang GT || Tech and Talk > 2005-2010 Mustang GT

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
what are the advantages of a tune when you have a 5 speed ? jrny99 2011-2014 Mustang GT 3 02-26-2012 09:03 PM
Time to Shine, off to the Body Guy Jeffola 2011-2014 Mustang GT 23 02-26-2012 11:23 AM
Sct tuner tbonestang AmericanMuscle 24 02-26-2012 10:33 AM
SCT tuner owners help me out! Project Pony Pre-2005 V6 Mustang 25 02-26-2012 12:45 AM
Speedo recalibrate McNassty SVT Mustang 8 02-24-2012 07:16 PM

» Like Us On Facebook



04:50 PM


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Content Relevant URLs by vBSEO 3.6.0

MustangEvolution.com is in no way associated with or endorsed by Ford Motor Company.